Phase and amplitude equalization arrangement

Abstract

An equalisation arrangement compensates for multipath phase and amplitude distortion effects in a transmission channel by first measuring such distortion effects as they occur over time in a calibration phase, thereby obtaining phase and amplitude compensation factors, then applying these factors to a correcting circuit situated in the signal path of the receiver at the appropriate times during a subsequent data transmission phase. Calibration is achieved by feeding a received calibration signal to an amplifier, preferably a successive detection logarithmic amplifier (26), comparing the phase of the limited linear output of the logarithmic amplifier with a delayed version of itself (30, 28), and using the amplitude information (39) in the logarithmic output (72) of the logarithmic amplifier (26) and the phase-change information (35) resulting from the phase comparison to compute the phase and amplitude compensation coefficients. In the data transmission phase, the compensation coefficients are applied to amplifiers and multipliers, etc (56, 55), in the correcting circuit.

I claim: 
     
       1. An equalization arrangement for use in a receiver for the correction of phase and amplitude distortion effects, comprising: amplifying means for amplifying a signal received along a received signal path by the receiver, said amplifying means having an input fed by the received signal and first and second outputs representative of the amplitude and phase, respectively, of the signal at the input; phase detecting means for detecting a disturbance in the phase of the received signal, said phase detecting means being fed from the second output of the amplifying means; and correcting means for correcting for the phase and amplitude distortion effects, said correcting means having first and second inputs, means connecting said correcting means in the received signal path of the amplifying means, means connecting said first and second inputs of said connecting means to the first output of the amplifying means and to an output of the phase detecting means, respectively, said correcting means being arranged to adjust the amplitude and phase of the received signal in response to disturbances in amplitude and phase detected by the amplifying means and phase detecting means, respectively. 
     
     
       2. The equalization arrangement as claimed in claim 1, in which the phase detecting means comprises a phase detector, a delay line, means connecting one end of the delay line to a first input of the phase detector and means connecting another end of the delay line to a second input of the phase detector and to the second output of the amplifying means. 
     
     
       3. The equalization arrangement as claimed in claim 1, in which the amplifying means is a successive detection logarithmic amplifier, the first output of the amplifying means being constituted by the detected logarithmic output of the logarithmic amplifier, and the second output of the amplifying means being constituted by the limited linear output of the logarithmic amplifier. 
     
     
       4. The equalization arrangement as claimed in claim 1, in which the correcting means comprises a storage means for storing quantities related to the magnitudes of amplitude and phase disturbances that occur in a calibration signal received by the receiver during a calibration phase, and retrieval means for retrieving said quantities during a later compensation phase and using them to correct for amplitude and phase disturbances in a data signal received by the receiver during the compensation phase. 
     
     
       5. The equalization arrangement as claimed in claim 4, in which the correcting means further comprises analogue-to-digital converting means for converting the magnitudes of the amplitude and phase disturbances from the amplifying means and phase detecting means, respectively, into digital form, and a processing means for deriving therefrom correction coefficients for storage in the storage means. 
     
     
       6. A method of correcting for amplitude and phase distortion effects in a transmission system having a calibration phase and a compensation phase, comprising the steps of: a) during said calibration phase: transmitting a calibration signal; receiving the calibration signal over a received signal path and feeding the calibration signal to an amplifying means, said amplifying means providing on separate outputs signals representative of the amplitude and phase, respectively, of the received calibration signal; detecting in a phase detecting means a disturbance in the phase of the signal at the phase output of the amplifying means; deriving from the amplitude output of the amplifying means and from an output of the phase detecting means amplitude and phase compensation signals for use during the compensation phase, the compensation signals being related to disturbances in amplitude and phase as they occur over time, and   b) during said compensation phase: applying, over time, said compensation signals to a correcting means connected in the received signal path of the received signal such as to compensate for said phase and amplitude distortion effects.   
     
     
       7. The method as claimed in claim 6, in which the compensation signals are used to adjust amplitude and phase characteristics of correcting elements within the correcting means. 
     
     
       8. The method as claimed in claim 7, further comprising the step of storing quantities corresponding to the magnitudes of the compensation signals during the calibration phase and retrieving those quantities during the compensation phase. 
     
     
       9. The method as claimed in claim 8, further comprising the step of converting the magnitude quantifies of the compensation signals into digital form, deriving compensation coefficients from said digital quantities, and storing said coefficients for retrieval during the compensation phase. 
     
     
       10. The method as claimed in claim 6, in which the phase detecting means detects a disturbance in the phase of the received signal by comparing, in a phase detector, the phase output of the amplifying means with a delayed version of itself. 
     
     
       11. The method as claimed in claim 6, in which the calibration signal is a channel sounding pulse transmitted separately from data. 
     
     
       12. The method as claimed in claim 6, in which the calibration signal is a preamble transmitted at the head of a data string, the preamble having known phase and amplitude characteristics.